1. Field of the Invention
The present invention relates to an actuator array which causes displacement based on an electric/mechanic energy conversion using an electric field induced strain such as an inverse piezoelectric effect. In more detail, the present invention relates to a piezoelectric actuator array which is preferably used in an optical switch, optical shutter, optical micro-device such as a mirror array, image display apparatus, high frequency filter, micro-pump, droplet discharge apparatus, and the like and which achieves both a high generation force and large displacement and in which a piezoelectric member causing the displacement has a high aspect ratio superior in consistency of the generation force and displacement and which is easily handled and positioned, and also relates to a manufacturing method of the actuator array.
2. Description of the Related Art
In recent years, in an optical field, precision machine field, semiconductor manufacturing field, and the like, there has been a demand for a displacement control device which adjusts an optical path length or position in an order of sub-microns. To meet this demand, development of an actuator has been advanced in which a strain is used based on an inverse piezoelectric effect or electrostrictive effect caused at a time of application of an electric field onto a ferroelectric or antiferroelectric material. As compared with a conventional electromagnetic system by a servo motor, the displacement control device using these electric field induced strains has characteristics that micro displacement is easily controlled, an electric/mechanic energy conversion efficiency is high to save power, and the device can be mounted with an ultra precision and can contribute to the miniaturizing/lightening of products. Applied fields are assumed to be enlarged.
For example, in the optical switch, the use of a piezoelectric actuator as an actuator portion for switching a transmission path of input light has been proposed. One example of the optical switch is shown in FIGS. 20(a), 20(b). An optical switch 200 shown in FIGS. 20(a), 20(b) includes a light transmission portion 201, optical path-changing portion 208, and actuator section 211. In detail, the light transmission portion 201 includes a light reflection surface 101 disposed partially in a surface disposed opposite to the optical path-changing portion 208, and light transmission channels 202, 204, 205 disposed in three directions from the light reflection surface 101 which is a start point. The optical path-changing portion 208 is disposed in the vicinity of the light reflection surface 101 of the light transmission portion 201 in a movable state, and includes a light introduction member 209 formed of a translucent material, and a light reflection member 210 which totally reflects light. Furthermore, the actuator section 211 includes a mechanism which is displaced by an external signal and which transmits the displacement to the optical path-changing portion 208.
In the optical switch 200, as shown in FIG. 20(a), the actuator section 211 operates by an external signal indicating the application of a voltage, and the optical path-changing portion 208 is detached from the light transmission portion 201 by the displacement of the actuator section 211. A light 221 inputted in the light transmission channel 202 of the light transmission portion 201 does not pass and is totally reflected by the light reflection surface 101 of the light transmission portion 201 whose refractive index is adjusted to a predetermined value, and is transmitted to the light transmission channel 204 on the output side.
On the other hand, conversely, the actuator section 211 is brought into an inoperative state from this state. Then, as shown in FIG. 20(b), the displacement of the actuator section 211 returns to an original state, and the light introduction member 209 of the optical path-changing portion 208 contacts the light transmission portion 201 at a distance which is not more than a wavelength of the light. Therefore, the light 221 inputted into the light transmission channel 202 is taken out into the light introduction member 209 from the light transmission portion 201 by the light introduction member 209, and passes through the light introduction member 209. The light 221 transmitted through the light introduction member 209 reaches the light reflection member 210. However, the light reflected by the a reflective surface 102 of the light reflection member 210 is transmitted to the other light transmission channel 205 on an output side, different from the light reflected by the light reflection surface 101 of the light transmission portion 201.
In the above-described optical switch, in order to enhance a performance, first, there is a demand for a large ON/OFF ratio (contrast). In order to set the ON/OFF ratio (contrast) to be large, in the optical switch 200, it is important to securely perform a contact/release operation with respect to the light transmission portion 201 of the optical path-changing portion 208. The actuator section preferably takes a large stroke, that is, is largely displaced.
To further enhance the performance, there is a demand for reduction of a loss in the switching. In this case, it is important to increase a substantial contact area with respect to the light transmission portion 201 while increasing the area of the optical path-changing portion 208. Moreover, the increase of the contact area is a factor for drop of certainty in the releasing, and therefore the actuator section needs to be capable of generating a large force.
That is, for the enhancement of the performance of the optical switch, as the actuator section, there has been a demand for a piezoelectric actuator in which the displacement can be consistent with the generation force. Additionally, in the optical switch, in future, with advancement in construction of an optical network system which does not perform optical/electric conversion, the number of channels of a photonic router increases, whereas the photonic router is requested to be further miniaturized. Therefore, there is a demand for high integration in the optical switch which is one constituting element of the photonic router.
However, in the piezoelectric actuator in which a plurality of piezoelectric devices of a uni-morph or bimorph type which has heretofore been known are arranged (these will hereinafter be referred to as the flexure displacement devices) a slight contraction strain of the piezoelectric device itself at the time of the electric field application is converted to a flexure mode to form the flexure displacement. Therefore, it is easy to obtain a large displacement in proportion to a device length of the piezoelectric device. However, since the strain is converted, a generated stress applied to the directly generated strain of the piezoelectric device cannot be used as such. It is very difficult to enlarge the generation force simultaneously with the displacement.
Moreover, in the flexure displacement device, a plate piezoelectric member is constituted/disposed substantially vertically to a displacement direction. Therefore, a device dimension (width or thickness) naturally and inevitably increases, and it is therefore difficult to dispose the device in a high density while reducing the pitch.
The actuator in which the piezoelectric devices are arranged in the high density has heretofore been proposed (e.g., see Japanese Patent No. 3058143 specification, especially FIG. 1 thereof; hereinafter referred to as Patent Document 1). The piezoelectric actuator in Patent Document 1 is optimum for an ink jet system recording apparatus, and is disclosed as a piezoelectric actuator in which pillar-shaped piezoelectric devices functioning as a driving organization are arranged in a grid pattern in a planar form and can be arranged in high integration. Moreover, the piezoelectric actuator is reported to have an effect that the number of ink jet nozzles per unit area in the recording apparatus of the ink jet system can be increased.
However, for the disclosed piezoelectric actuator, green sheets coated beforehand with common or application electrodes are stuck and sintered, and thereafter grooves are processed by a dicing saw in order to independently separate the pillar-shaped piezoelectric devices from one another. Therefore, there are at least two problems as follows.
First, the electrode includes a structure housed beforehand in the piezoelectric device, and is therefore influenced by the strain at a sintering time. A layer structure including the electrode-piezoelectric member of each independently separated piezoelectric device easily becomes uneven, and there is a problem that fluctuations of characteristics are caused among the devices. Additionally, considering from the sintering strain, the device dimension (width or thickness) naturally and inevitably increases, and it is therefore difficult to reduce the pitch. According to a disclosed mode example, the piezoelectric device has a width of 0.3 mm, the groove has a width of 0.209 to 0.718 mm, and the density has a degree of one piezoelectric device disposed per about 1 mm2. However, this cannot easily be said to be a sufficient integration for handing a resolution which has been required for an ink jet printer in recent years. The integration cannot be satisfactory even in the optical switch whose one mode example is shown in FIGS. 20(a), 20(b).
Next, in the disclosed piezoelectric actuator, the independently separated piezoelectric devices are formed by the dicing saw processing, but there is a problem that a depth of the groove, that is, a height of the piezoelectric device is inevitably reduced/limited by processing restrictions. For a lateral effect device in which the generated displacement depends on the height of the piezoelectric device, when the height is limited, the obtained displacement is not sufficient. That is, in the disclosed piezoelectric actuator, it is impossible to increase an aspect ratio (height/thickness) of the piezoelectric device (piezoelectric member) which is an index of high integration and high characteristic. Therefore, the actuator is not preferable not only for the ink jet printer but also for the actuator section of the optical switch.